Modeling of Borehole Hydraulic Fracture Initiation and Propagation with Pre-existing Cracks Using the Displacement Discontinuity Method

Pre-existing borehole cracks result in hydraulic fracture deflection, which causes sand screen-out in advance and even fracturing failure. Based on a simplified three-dimensional displacement discontinuity method, a model to simulate the initiation and propagation of hydraulic fractures from a borehole with pre-existing cracks was established. It is found that the effects of injection rate and fracturing fluid viscosity on fracture propagation are similar. When the effects are smaller, hydraulic fractures quickly turn perpendicular to the minimum horizontal stress. With injection rate or viscosity increase, the injection pressure at the well bottom increases, and the turning degree and width of hydraulic fractures increase. The length of pre-existing cracks dramatically affects the breakdown pressure. With increasing pre-existing crack length, the breakdown pressure decreases. With increasing horizontal stress contrast, the hydraulic fracture path clearly changes, and the required extension pressure also increases when the injection rate and fracturing fluid viscosity both remain constant.